The present invention relates to electron optical systems and, more particularly, to a novel improved magnetic fine deflection system for use with matrix lens electron optical systems.
Modern data processing requires high capacity memory of the random-access and/or read-only types, with the memory having extremely high bit storage density and permitting rapid data storage retrieval. Memory systems of this type are disclosed in U.S. Pat. No. 3,534,219, issued Oct. 13, 1970 and assigned to the assignee of the present invention; the entire disclosure thereof is incorporated herein by reference. As disclosed and claimed in the afore-mentioned U.S. Patent, a random-access memory of the storage tube type utilizes an electron beam focusing and positioning system of the type having a coarse deflection system for causing the electron beam source to be presented to a selected one of a plurality of electron lenses arranged in the form of a two-dimensional matrix, with a second (or fine) deflection assembly positioned between the matrix lens and the data-storage target for focusing the beam passing through each single lenslet on a desired specific point of the target structure. Further improvement in the electron optics of the storage system are disclosed and claimed in U.S. Pat. No. 4,070,597, issued Jan. 24, 1978 and U.S. Pat. No. 4,122,369, issued Oct. 24, 1978, both assigned to the assignee of the present invention and both incorporated herein by reference in their entirety. In the latter-mentioned pair of U.S. Patents, a single plate matrix lens, having a multiplicity of apertures, is utilized with a means positioned between the lens plate and target for accelerating the electrons to the target, and a fine magnetic deflection means positioned under-the-target, i.e. upon the side of the target furthest from the accelerating means, lens plate and the remainder of the electron optics column. The under-the-target magnetic deflection system, having an orthogonal set of sheet conductors positioned behind the target for producing the magnetic deflection field in the region between the matrix lens plate and the target, not only requires a relatively high magnitude of deflection drive current in the sheet conductors, but also generates a fine magnetic deflection field which penetrates into the lenslet selector region about the single lens plate and extends beyond the matrix lens, in the direction of the electron source, and into the coarse deflection region, thus preventing the coarse deflection means from deflecting the collimated electron beam precisely to the center of a desired one of the multiplicity of lenslets in the matrix lens and, consequently, reducing the current of the electron beam entering the fine deflection region. It is desirable to provide a magnetic fine deflection system for use with the matrix lens electron optics, but having a reduced deflection drive current requirement and preventing magnetic fields due to the fine magnetic deflection system from penetrating into, and beyond, the lenslet selector region at the matrix lens plate.